As part of the VSMC response to injury, VSMC migrate into the lumen of the vessel where they proliferate and synthesize cytokines which they respond to in an autocrine fashion, sustaining the loss of lumen diameter. In the course of HL63810, we have determined that expression of Allograft Inflammatory Factor-1 (AIF-1), a newly described cytoplasmic, calcium-binding protein, is predictive of development of clinical transplant vasculopathy. Expression of AIF-1 in injured carotid artery significantly exacerbates reduction of lumen diameter and recruits bone marrow cells to the adventitia. Knock-down of AIF-1 abrogates neointimal hyperplasia. Expression of AIF-1 in human VSMC increases migration, proliferation, induces expression of G-CSF, and activates the Pad GTPase. AIF-1 contains several signaling domains, binds to and polymerizes actin, and activates signal transduction proteins. Our data support our central hypothesis that AIF-1 is an inflammation-responsive scaffold protein that plays a key role in regulation of VSMC activation and development of neointimal hyperplasia. The overall goals of this application are to 1- determine a cause and effect relationship between AIF-1 expression and neointimal hyperplasia in vivo, and 2- characterize the cellular pathways and molecular mechanisms responsible for AIF-1 activity in VSMC. Three aims have been formulated to test the hypothesis that;1- AIF-1 expression exacerbates neointimal hyperplasia, and that reduction of AIF-1 expression will reduce neointimal hyperplasia in angioplasty-injured rats and AIF-1 transgenic mice, 2- that AIF-1 directly activates Rac1 signaling pathways leading to G-CSF expression, and that AIF-1 directly activates G-CSF expression with a subsequent autocrine activation of the Rac signaling pathway, and 3- AIF-1 activates Rac1 by activation of GEFs, and induces G-CSF expression by activation of transcription factors. Characterization of AIF-1 function will clarify our understanding of inflammation-mediated signal transduction leading to VSMC pathobiology and vascular- immune cell cross talk.